Cells derived from pluripotent stem cells, also referred to herein as embryonic stem cells (“ESC”), are being investigated as agents to repair or rejuvenate tissue. However when injected in vivo, ESC, due to their pluripotential, form teratomas, i.e. dysregulated, cancerous tumor growths.
To avoid generation of teratomas or disorderly growth in vivo, the ESC presently being developed for transplantation are differentiated ex vivo into lineage committed adult stem cell phenotypes and/or fully differentiated cells. This process is time consuming and generally requires maintenance of Good Manufacturing Procedures (GMP) over an extended period of time. The differentiated cells must be purified to ensure that there is no contamination from residual pluripotent ESC. The process must also include a method to ensure desired cell identity and lot-to-lot equivalency.
Transplanted ESC-derived cells produced by current methods require lifetime immune suppression to prevent immune mediated rejection of ESC-derived cells. Many immunosuppressants are also cytotoxic and include antimetabolites (azathioprine), alkylating agents (cyclophosphamide), and folic-acid antagonists (methotrexate or 6-MP). Other immunosuppressants include mycophenolate mofetil (CellCept® from Hoffmann-La Roche, Inc.) and cyclosporin. These drugs may cause numerous side effects including lethal infections.
Transplantation of ESC-derived cells requires the use of viable live cells that have a very limited shelf life. Maintaining cell viability requires local on site production for immediate infusion and or cryopreservation (freezing) in agents such as DMSO before overnight shipping on dry ice to prevent thawing. The frozen cells must then be thawed, washed to remove cytotoxic cryo-preservatives like DMSO, sterility rechecked, and viability reconfirmed before infusion, all of which increases expense and limits availability and practical application.